Data storage devices such as disk drives are used in many data processing systems. Typically a disk drive includes a magnetic data disk having disk surfaces with concentric data tracks, and a transducer head paired with each disk surface for reading data from and writing data to the data tracks.
Disk drive storage capacity increases by increasing the data density (or areal density) of the data stored on the disk surfaces. Data density is the linear bit density on the tracks multiplied by the track density across the disk surface. Data density is measured in bits per square inch (BPSI), linear bit density is measured in bits per inch (BPI) and track density is measured in tracks per inch (TPI). As data density increases, the head performance distribution also increases which diminishes disk drive storage capacity and yield.
Conventional disk drives fail to account for the different capabilities of the head and disk surface pairs. Conventionally, each disk surface is formatted to store the same amount of data as every other disk surface. However, each head and disk surface pair has unique data recording capability, such as sensitivity and accuracy, which depends on the fly height of the head over the disk surface, the magnetic properties of the head and the quality/distribution of the magnetic media for the disk surface. Thus, in conventional disk drives a head and disk surface pair that has a low error rate is formatted to the same BPI and TPI as a head and disk surface pair that has a high error rate.
Conventional disk drive manufacturing applies a single error rate and a single data storage level for the head and disk surface pairs, and scraps disk drives that include a low performing head and disk surface pair that fails to meet the qualifying requirements. This lowers storage capacity due to inefficient use of high performing head and disk surface pairs that can store more data, and lowers yield due to disk drives being scrapped if they include a low performing head and disk surface pair even if they also include a high performing head and disk surface pair.
U.S. Pat. Nos. 6,091,559 and 5,596,458 provide different BPI on different disk surfaces, however these approaches do not take into consideration multiple constraints, including head performance across the stroke per disk surface, performance requirements such as throughput and manufacturing requirements such as test time. Instead, disk surface zone frequencies are selected based on a single metric for one head.
There is, therefore, a need for storing data in a disk drive which improves disk drive storage capacity and yield and accounts for head performance variation.